With power-operated devices there is always the risk that objects or body parts are caught, which can cause damage to objects or injury to people. Since the use of motor driven devices is becoming more prevalent in order to enhance comfort, for example in doors, windows, and shutters in building services engineering or in windows, sliding roofs, and convertible tops in automotive engineering, an early and reliable detection of an obstruction situation becomes increasingly important, since the movement of those devices often takes place automatically and without being monitored by an operator.
For example, newer convertible vehicles are often equipped with a movable convertible top, which can be automatically moved for example from an open to a closed position or vice versa with the push of a button. The movement of the convertible top is usually effected by a hydraulic drive, which in turn drives a convertible top mechanism, which includes a convertible top linkage. The linkage may support for a textile roof or a so-called hard-top folding roof with mainly rigid roof elements, and may include a cover for a convertible top compartment as well as all elements that are being moved in the process by the described parts.
Furthermore it is common knowledge to provide a detection device with capacitive sensors in order to recognize an intervention into the range of motion of a motor driven device such as the convertible top.
Such an obstruction sensor with a capacitive sensor system is described in German Patent Application DE 198 36 056 A1, whereby the device that is being used to detect the obstructions, in particular when automatically closing convertible tops, vehicle windows or the like includes a capacitive sensor device, which consists of an electroconductive transmitter surface on one side and an electroconductive sensor wire and at least one metal surface that is mainly potential-free on the other side of an insulator. The transmitter surface and the sensor wire are connected to an electronic analysis circuit in the process.
However, the disadvantage of these kinds of obstruction sensor devices that operate with a capacitive sensor system is that they require a relatively large installation space and thus can not be used in all safety-relevant areas, which has the result that an obstruction situation may not be detected until very late in the process when making contact with the object that interferes with the range of motion, whereupon a corresponding reaction can be triggered.
German Patent Application DE 101 04 333 A1 describes a convertible vehicle with a convertible top which can be folded into a storage compartment, whereby the storage compartment is located in a rear part of the vehicle adjacent to a trunk and is separated from the trunk by means of a variable separation device. The separation device is movable between a convertible top storage position in which it limits the additional space and increases the storage compartment space, and a luggage storage position in which it limits the additional space and increases the trunk space, whereby the separation device comprises at least one movable plate element.
A capacitive sensor comprising a multitude of flat films is mounted on the plate element in order to avoid an obstruction in the additional space during convertible top movement. This type of sensor comprises two foils or plates arranged parallel to each other with a dielectric between. The dielectric is made out of a mechanically robust as well as elastically deformable material such as foamed material. A deformation of the sensor and thus a change of the distance between the foils or plates which can be measured as a change in capacitance that takes place when the sensor contacts a piece of luggage.
Although such a film-like sensor has the advantage to be flat in comparison with other sensors, the sensor needs to contact an obstacle in the path of motion. Therefore, also with this solution a reaction is late, especially in regard to an obstruction protection for body parts.
German Patent Application DE 40 11 901 A1 describes another capacitive sensor responding upon pressure, whereby a change in capacitance resulting from a deformation of two parallel plates is measured.
Other capacitive sensors are known from German Patent Publications DE19724168C1, DE19805928A1, and DE3236056A1.